The invention relates to a heat-resistant Al—Cu—Mg—Ag alloy for producing semi-finished parts or products, suitable for use at rather high temperatures and with high static and dynamic strength properties combined with an improved creep resistance. The invention also relates to a process for producing a semi-finished part or product composed of such an aluminum alloy.
An alloy of the above-cited type is known in EP 1 518 000 B1 from which semi-finished parts are produced with high static and dynamic strength properties, and an improved creep resistance in comparison to previously-known, similar aluminum alloys. This alloy is registered with the Aluminum Association (AA) as alloy AA2016. This previously-known alloy already approximately unites the strength properties necessary for semi-finished parts and products that must resist high static and dynamic loads. These properties are known from the alloys AA2014, AA 2014A or AA2214 and have an improved creep resistance, which is an improved resistance under the action of temperature. The alloy AA2016 therefore satisfies the claims put on semi-finished parts and products produced from them that are exposed for a short time to elevated temperatures, for example as in the wheel halves of airplanes. These semi-finished products are exposed to elevated temperatures only during braking after the airplane sets down on the landing strip.
The alloys AA2618 and AA2618A are considered to be especially creep-resistant. However, semi-finished parts and products produced from these alloys have only relatively low static and dynamic strength values.
The alloys for producing semi-finished parts with high static and dynamic strength properties in accordance with AA2014, AA2014A and AA2214 differ chemically from the alloys with long-time thermal stability according to AA2618 and AA2618A. This is because the very strong aluminum alloys contain relatively high amounts of the elements silicon, copper and manganese and relatively low amounts of the elements magnesium and iron, whereas the long-time thermally stable aluminum alloys have a reduced amount of silicon, copper and manganese in contrast to the above and an elevated content of iron, nickel and magnesium. In addition, nickel is mixed into the long-time thermally stable alloys.
The alloy AA2016 differs from the previously described alloys in particular by an admixture of the element silver with amounts between 0.30 and 0.7 wt %. There are also differences in the remaining alloy elements in comparison to the composition of both the previously-cited very strong aluminum alloys, and the previously-cited aluminum alloys whose semi-finished parts have a good creep resistance.
Even if the aluminum alloy AA2016 is known to produce semi-finished parts and products that can satisfy high static and dynamic strength requirements and also resist elevated temperatures in short-time use, there has long been a desire to have available an aluminum alloy for producing semi-finished parts and products that resist elevated temperatures for longer-term use. Such requirements are placed on a plurality of products, for example, on the compressor wheels of a turbocharger in motor vehicle engine uses. These structural components must not only resist high static and dynamic loads, but also the high temperatures prevailing in such a use for the duration of the use. Similar requirements for long-time stability at rather high temperatures are also applicable to turbocharger compressors of large engines in ship construction.